1. Field of the Invention
The present invention relates generally to mold-release agents for mold surfaces and, more particularly, to a method for forming a mold-release coating using a release powder electrostatically deposited on a mold surface.
2. Description of the Related Art
In the process of making molded polymeric foam parts, such as polyurethane foam parts, foam precursor material is first admitted into a mold and, subsequently, the foam precursor material is caused to foam and cure, taking on the shape of the mold's interior.
The interior surfaces of the mold are usually coated with a wax mold-release agent before every molding operation. The wax mold-release agent allows complete and easy removal of the molded part. Typically, the wax mold-release agent is spray-applied onto the mold surface.
Current wax mold-release agents include solvent-based and water-based agents. Solvent-based wax mold release agents are applied to the interior surface of molds and allowed to dry. These agents are applied before every molding operation or frequently between molding operations. However, during the drying step, volatile organic compounds are evolved, requiring precautions to avoid human exposure. With the increased awareness of environmental protection, such solvent-based wax mold-release agents are becoming obsolete.
Water-based wax mold-release agents result in substantially less evolution of volatile organic compounds than do the solvent-based wax mold-release agents. Water-based wax mold-release agents are also applied before every molding operation or frequently between molding operations. Although they contain much less volatile organic compounds than solvent-based wax mold-release agents, water-based wax mold-release agents are not without problems.
One problem with water-based wax mold-release agents is that they still contain a small amount of volatile organic compounds which are evolved during the coating process. Secondly, water-based wax mold-release agents gradually build-up on the mold surface causing undesirable changes in the mold's dimensions or contours. Thirdly, water-based wax mold-release agents are more expensive than solvent-based wax mold-release agents. Lastly, water-based wax mold-release agents require longer drying times than do solvent-based wax mold-release agents.
A problem with using a mold release agent is that there remains wax deposit on the surface of the part after removal, along with wax build-up on the mold itself.